There has long been a need for materials which combine the desirable qualities of reasonable strength, good stiffness and load carrying ability, and good sound and temperature insulation with substantially less weight than solid members of the same materials. Most of such structures are of a type known as honeycomb materials. Such materials are often formed of numerous connected cells of organic material such as paper or wood as the internal structure with wood, glass fiber, or metal exterior plates fastened to the ends of the cells, typically with a suitable glue such as an epoxy resin. All metal honeycomb structure is also known wherein interconnected cells of thin wall metal are fastened by suitable means, to exterior plates. Such a honeycomb structure is shown and described in U.S. Pat. No. 4,013,210. This patent also describes a vacuum diffusion bonding process for fastening the metal honeycomb structure to face sheets or plates. The process and resulting product seem to be directed principally to forming titanium bodies. Other patents teach the use of epoxy of some type as the bonding media, e.g. U.S. Pat. Nos. 4,692,367 and 4,063,981. U.S. Pat. No. 4,622,445 teaches a process for brazing a metal face sheet to a honeycomb core wherein a brazing alloy is placed between the face sheet and the core and the face sheet pressed to the core with a piece of thermal insulation while the metal parts are heated to a temperature just sufficient to melt the brazing alloy. An inert gas is provided as an environment during the heating process.
The problem with such honeycomb structures is that, in general, they are relatively fragile; if bonded with epoxy they are quite limited in the temperature and atmospheric pressure changes to which they may be exposed, they cannot normally be made thinner than about 0.25 inch, and once so constructed they cannot be processed further to conform to other shapes, as by rolling, forming, bending, etc. Due to temperature or pressure stress, delamination often occurs causing moisture absorption resulting in internal corrosion. There is a need for an all metal laminated structure providing good sound and thermal insulation which is essentially as strong as a homogeneous metal panel of the same thickness, but substantially lighter in weight, which is essentially immune to internal corrosion, which can be subjected to essentially all the same metal forming processes as homogeneous metal, which may be repaired or fabricated by welding similarly to homogeneous metal, and in which any cuts or punctures affect only the cells directly involved because each entrained cell is effectively vacuum sealed from all the others.